Shorten PR template checklist (opensearch-project#13979)

This commit removes items from the checklist that were redundant in
order to reduce the work required to submit a PR. This also removes the
check that enforces checklist completion as requested by issue opensearch-project#10970.

Resolves opensearch-project#13965
Resolves opensearch-project#10970

Signed-off-by: Andrew Ross <[email protected]>
(cherry picked from commit ac78f0a)

.github/pull_request_template.md

@@ -1,18 +1,21 @@
+<!--  Thanks for sending a pull request, here are some tips:
+
+1. If this is a fix for an undisclosed security vulnerability, please STOP. All security vulnerability reporting and fixes should be done as per our security policy https://github.com/opensearch-project/OpenSearch/security/policy
+2. If this is your first time, please read our contributor guidelines: https://github.com/opensearch-project/OpenSearch/blob/main/CONTRIBUTING.md and developer guide https://github.com/opensearch-project/OpenSearch/blob/main/DEVELOPER_GUIDE.md
+3. Ensure you have added or ran the appropriate tests for your PR: https://github.com/opensearch-project/OpenSearch/blob/main/TESTING.md
+-->
+
 ### Description
 [Describe what this change achieves]
 
-### Issues Resolved
-[List any issues this PR will resolve]
+### Related Issues
+Resolves #[Issue number to be closed when this PR is merged]
+<!-- List any other related issues here -->
 
 ### Check List
-- [ ] New functionality includes testing.
-  - [ ] All tests pass
-- [ ] New functionality has been documented.
-  - [ ] New functionality has javadoc added
-- [ ] Failing checks are inspected and point to the corresponding known issue(s) (See: [Troubleshooting Failing Builds](../blob/main/CONTRIBUTING.md#troubleshooting-failing-builds))
-- [ ] Commits are signed per the DCO using --signoff
-- [ ] Commit changes are listed out in CHANGELOG.md file (See: [Changelog](../blob/main/CONTRIBUTING.md#changelog))
-- [ ] Public documentation issue/PR [created](https://github.com/opensearch-project/documentation-website/issues/new/choose)
+- [ ] Functionality includes testing.
+- [ ] API changes companion pull request [created](https://github.com/opensearch-project/opensearch-api-specification/blob/main/DEVELOPER_GUIDE.md), if applicable.
+- [ ] Public documentation issue/PR [created](https://github.com/opensearch-project/documentation-website/issues/new/choose), if applicable.
 
 By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.
 For more information on following Developer Certificate of Origin and signing off your commits, please check [here](https://github.com/opensearch-project/OpenSearch/blob/main/CONTRIBUTING.md#developer-certificate-of-origin).